55MHz Scope Sensitivity Amplifier

Scope sensitivity amplifier is a vital front-end signal processing for every scope instruments. The function of this circuitry is simple: amplify the signal with a consistent/stable gain without altering the waveform. A stability of its gain make it possible to make a precise volts/div scaler with no drift in time and ambient temperature. The requirement to reproduce the signal without altering the waveform sounds very simple, but it means that the amplifier circuit must have very low distortion level in processing dynamic signal. For such requirement, a low input noise LM733 video amplifier can be used to build a scope sensitivity amplifier. With a good frequency response within 0.5 to 25 MHz range, the voltage gain of this circuit is 20 ±0.1 dB. If we need to extend the frequency range between 70 kHz to 55 MHz, we need to limit the voltage gain at maximum ±3 dB to give a flat response. The R1 is used to adjust the scale factor so that the circuit can provide voltage gain of 100. The other way to produce 100 voltage gain is by replacing the resistor with selected precision resistor. Here is the schematic diagram of the circuit: